The primary objective of this study was to examine the effect of breed, lactation and grazing period on the cis 9, trans 11-Conjugated Linoleic Acid (c9,t11-CLA) and trans 11-Vaccenic Acid (VA) levels in cow's milk. The secondary objective was to compare the properties of cheese products made from the study milk to commercially available cheeses. Milk samples from a commercial dairy farm representing 3 breeds (Fleckvieh Cross, n=19; Holstein, n=18; Jersey, n=12) were analyzed at three points in the grazing period. Daily yield, CLA yield, VA, yield and the percentage of VA in milk were greatest in June, intermediate in July and lowest in September. The percentage of c9,t11-CLA in milk was lower in September compared to June and July. The VA and c9,t11-CLA content of cheese made from the milk samples were ~2-fold higher than commercially available samples of Cheddar and ~1.5-fold higher than commercially available samples of Mozzarella. In conclusion, the c9,t11-CLA and VA contents of milk decrease over the June through September grazing period, likely due to the grazing material.